1. Field of the Invention
This invention generally relates to a color image processing system for processing color image data to be used in forming a color image, and, in particular, to a color image processing system having an adjustable under color removal (UCR) function suitable for use in color copiers and color printers.
2. Description of the Prior Art
In various imaging apparatuses, including copier and printers using an electrophotographic process, such as laser beam printers, thermal printers and ink-jet printers, it is often desired to produce a color image. Here, such an imaging apparatus capable of producing a color image will be referred to as a color printer. In a color printer, a color image may be formed by using three coloring materials, i.e., cyan, magenta and yellow; however, use is often made of black in addition to these three coloring materials. In such a color printer using four coloring materials, i.e., cyan, magenta, yellow and black, the image data for black color component is created by applying an under color removal (UCR) process based on the image data for each of cyan, magenta and yellow in order to print the black color component.
In the prior art UCR process, the black component is printed first and then the three color components of cyan, magenta and yellow are printed as superimposed on the black color component. For this reason, in accordance with the prior art UCR process, the image data of each of cyan, magenta and yellow is once stored in a frame memory of the corresponding color component, and, then, the image data is read out of each of the frame memories to find the minimum value for the same pixel, if it is an UCR process having a 100% UCR rate. And, then, the minimum value thus found is subtracted from each of the corresponding image data read out of cyan, magenta and yellow frame memories to produce a modified image data which is then stored into a corresponding frame memory as a print data. On the other hand, the thus found minimum value is stored into a frame memory for black color component as a print data for printing a black pixel. In this manner, print data for black color is obtained for the entire page and then the black print data is used to print black color component first. And, then, the remaining color components of cyan, magenta and yellow are printed one after another to produce a color image using four coloring materials. In this manner, in accordance with the prior art UCR process, since black print data must be created so as to print a black color component, the UCR process is slow, which tends to slow down the overall imaging speed.